This invention relates to the field of measurement of load or weight on a cable. More particularly, this invention relates to a cable tensiometer, referred to herein as a weight beam, for measuring line tension in a cable, particularly a wire rope, to determine the weight or load being carried by the cable.
There are many applications and situations in which it is both desirable and important to accurately measure the load being carried by a cable, such as a wire rope. One field in which this information is very important is the oil well drilling field; and while this invention is by no means limited to use in that field, it will be discussed in relation to that environment for purposes of illustration and explanation.
In the oil well drilling field, it is important to know and monitor the total hook load acting on the draw works of the drilling rig to know the weight on the drill bit. In the prior art, this data is typically obtained by the use of devices which measure the tension in the cable by means of a mechanism at the dead line anchor. Cable tension has also been measured by a hydraulic load cell, in which the load cell is loaded in compression. However, the devices of the prior art have a number of drawbacks, in that they are relatively complicated, or are subject to error, or do not have dependable repeatability, or may require special tooling. One feature of the prior art hydraulic load cell devices which contributes to their deficiencies is that they measure a compression load on the sensing element to determine the tension in the cable; and this introduces potential inaccuracies and errors in these prior art systems.